Conventionally, transmission/reception of packets has been carried out based on a communication method referred to as “packet communication method” in a computer network. Recently, there has been a great demand for construction of LAN (Local Area Network) using PLC (Power Line Communication) in a home LAN.
Unlike the wired LAN, the LAN based on PLC does not require any special LAN cable to be wired and allows for construction of a network merely by connecting a power source cable of a device to a plug, so that this results in such advantage that a terminal can be more freely moved.
As to the LAN or the like based on PLC, in case of connecting a plurality of slave stations to a network in which a master station manages a bandwidth, a single network medium is shared by the plurality of slave stations in a time-division manner regarding transmission/reception of packets. In such a system, an efficiency at which the bandwidth is utilized greatly varies depending on how to manage transmission rights of the respective slave stations.
<QoS Technique>
Incidentally, in transferring non real-time data such as Web content item, mail, FTP, and the like, occurrence of certain transfer delay or jitter does not raise so significant problem. However, in transferring real-time data such as video, sound, and the like, transfer delay or jitter causes the video or the sound to be disarranged, so that it is necessary to suppress the transfer delay or the jitter to a certain level.
A technique for simultaneously and efficiently realizing transfer of plural data pieces in accordance with types of data pieces while keeping appropriate quality is referred to as “QoS (Quality of Service) technique.” The QoS technique is roughly categorized into “Prioritized QoS” and “Parameterized QoS”.
<Prioritized QoS>
In the Prioritized QoS, a communication apparatus for transmitting data gives a packet of data a priority according to a type of the data and a characteristic of a communication apparatus for transmitting/receiving the data so as to preferentially control transmission in accordance with the priority given to the packet, thereby realizing QoS.
Generally, a field for storing therein the priority is provided in a header of the packet, and a numerical value indicative of the priority is stored therein.
For example, higher transfer quality is required in transferring real-time data than in transferring non real-time data, so that a numerical value indicative of a higher priority is stored in the priority field of the header of the real-time data than in the priority field of the header of the non real-time data, and transmission is carried out in accordance with the priority corresponding to the numerical value, thereby realizing QoS.
<Parameterized QoS>
In the Parameterized QoS, a master station for managing a bandwidth of the entire network is provided, and the master station manages a schedule for using the bandwidth of the entire network in accordance with QoS parameters requested by slave stations, and all the slave stations are collectively managed in terms of the number of times of transmission and a transmission time, thereby realizing QoS.
In case of carrying out transfer whose QoS is guaranteed, a slave station preliminarily transmits a signal which requests for QoS transfer. This request signal includes a QoS parameter, and the master station interprets the QoS parameter, so as to determine whether QoS can be realized or not in accordance with a current status in which the network is used. If it is determined that QoS can be realized, the master station permits the QoS transfer. If it is determined that QoS cannot be realized, the master station refuses.
For example, in case where other slave station is carrying out QoS transfer and a sufficient bandwidth does not remain, the master station refuses the QoS transfer.
The master station always manages the schedule for allocating bandwidth so that QoS is guaranteed for each slave station and transmits a transmission permission signal to each slave station in accordance with the schedule. The slave station transfers data only in a period notified by the transmission permission signal.
In this way, there is no competition for access in the entire network, so that QoS is realized.
In the Parameterized QoS, QoS is managed for each flow. The flow refers to a series of data pieces required to be continuously transferred, e.g., video content, sound content, and the like. A plurality of packets belong to the series of data pieces.
In case of simultaneously transferring a plurality of content pieces, it is necessary to carry out QoS control in different manners corresponding to the content pieces respectively. For example, in case where a single communication apparatus simultaneously transmits video content and sound content, these content items are different from each other in terms of what is required in QoS.
The master station has to determine a schedule for using a bandwidth for each flow, so that it is necessary to find (i) a flow to which the packet belongs and (ii) a QoS parameter required, in transmitting the packet.
In order to realize QoS for each flow, the slave station notifies the master station of the QoS parameter together with flow identification information. The master station manages the schedule for using a bandwidth for each flow. In transmitting a transmission permission signal, the master station notifies also the flow identification information so as to show which flow corresponds to the transmission permission. The communication apparatus for carrying out the transmission transmits only a packet corresponding to the flow identification information, so that it is possible to control QoS for each flow.
The flow identification information is a part or a combination of: a receiving-end MAC address and a transmitting-end MAC address in a MAC header; a receiving-end IP address and a transmitting-end IP address in an IP header; a receiving-end port number and a transmitting-end port number in a TCP header (or a UDP header); a Flow Label field in an IPv6; a VID (VLAN Identifier) field of a VLAN tag in a frame header of Ethernet (registered trademark); and the like.
It is general to use the VID field of the VLAN tag not to virtually dividing LAN but to identify a flow.
In case of separating IP phone data and ordinary data (Web or FTP) from each other for example, physical separation thereof might be possible, but this is substantially impossible. Thus, it is general to carry out virtual separation with VLAN (a physically connected cable is shared but these data pieces are regarded as belonging to respective networks). For example, a first VID is allocated to transfer of the IP phone data, and a second VID is allocated to transfer of the ordinary data.
<How to Set QoS>
Generally, QoS is realized in a layer 2 or a layer 3 of an OSI reference model. Hereinafter, a layer for realizing and controlling QoS is referred to as “QoS control layer”.
In both the Prioritized QoS and the Parameterized QoS, the QoS control layer has to find transfer quality, required in transferring data, in order to realize QoS. However, it is general that such information is managed by a superordinate layer of the QoS control layer.
For example, the bandwidth control in PLC is realized by a MAC layer (a sub layer of the layer 2 in the OSI reference model), but what data is actually transferred can be found only at an application layer (a layer 7 in the OSI reference model).
For example, a program causes a content item to be selected and causes a preparation for transfer to be made at the layer 7 and then the data is passed to a subordinate layer, but the data passed from the superordinate layer is nothing but data for the subordinate layer and it is impossible to find its detail content and cannot find a program from which the data derives.
Thus, it is preferable that, before starting transfer of the data, the superordinate layer should request the QoS control layer to set QoS with information indicative of a program which the data is derived from and of a purpose of use thereof. However, mechanism of QoS has not been so widely known, so that the subordinate layer is not designed on the assumption that the subordinate layer is applied to QoS. Thus, mechanism of the notification has not been incorporated into most of systems.
<Regarding QoS Setting from a Terminal Connected to a Bridge Apparatus>
Further, in order to connect an apparatus equipped with an Ethernet interface (the apparatus is referred to as “Ethernet terminal”) to the PLC network, it is necessary to connect a bridge apparatus to the Ethernet terminal so that the Ethernet terminal is connected to the PLC network via the bridge apparatus. In case where the Ethernet terminal is to transfer data whose QoS has been secured in a PLC network interval in response to a received flow, the Ethernet terminal transmits any instruction to the bridge apparatus, and the bridge apparatus sets QoS of the PLC network in accordance with the instruction. For example, it is general to transmit an Ethernet packet indicative of such instruction from the Ethernet terminal to the bridge apparatus so as to control QoS.
<Regarding Patent Document 1>
Patent Document 1 describes mechanism for the user to specify a priority of Prioritized QoS in order to solve the problem.
In a home network connected to the CATV network, a MAC address of an information communication device connected to the home network and a transfer priority for the information communication device are preliminarily inputted by the user to a cable modem apparatus. As to the MAC address, the user refers to an instruction manual or checks out in a similar manner so as to find the MAC address.
In the cable modem apparatus, the inputted information is reserved as a control table, and the MAC address of a receiving end or a transmitting end in the home network is compared with the MAC address reserved in the control table so as to derive a priority of the packet, and an order of processes is changed in accordance with the priority, thereby realizing the Prioritized QoS for each information communication device.    Patent Document 1: Japanese Unexamined Patent Publication Tokukai 2003-153221 (Publication date: May 23, 2003)